Method for purifying actinides which are in low oxidation states

Abstract

A method is provided for purifying actinides which are present in a low oxidation state in aqueous solution. The actinides are purified of fission products by extracting the actinides from aqueous solution while confining the fission products to the aqueous solution. The actinides that are purified are selected from the group of uranium (IV), neptunium (IV) and plutonium (III). An aqueous nitric acid solution containing the actinides, hydrazine nitrate or hydroxyl ammonium nitrate, as well as fission products is initially subjected to an electrolysis voltage. If Pu (III) is involved, the electrolysis voltage is below the voltage at which oxygen develops at the anode and anodically oxidizes the Pu (III) to Pu (IV). The Pu (IV) which is formed is transferred by means of an organic extraction agent from the aqueous solution to an organic phase. The organic phase is then separated and used for the plutonium recovery process. If U (IV) and/or Np (IV) are involved, the aqueous nitric acid solution is initially subjected to an electrolysis voltage in the vicinity of the voltage at which oxygen develops at the anode or higher to anodically oxidize the U (IV) to U (VI) and the Np (IV) to Np (VI). The U (VI) and/or Np (VI) which is formed is transferred by means of an organic extraction agent from the aqueous phase to the organic phase. The organic phase is then separated and used for the uranium or neptunium recovery process.

What is claimed is: 
     
       1. A method for purifying plutonium present in a low oxidation of Pu(III) in an aqueous solution containing fission products by extracting the plutonium from the aqueous solution and confining the fission products to the aqueous solution comprising: subjecting an aqueous nitric acid solution containing the Pu(III), hydrazine nitrate or hydroxyl ammonium nitrate, and fission products to an electrolysis voltage below the voltage at which oxygen develops at the anode to anodically oxidize the Pu(III) to Pu(IV), transferring the Pu(IV) which was formed by anodic oxidation from the aqueous solution to an organic phase by means of an organic extraction agent separating the organic phase from the aqueous phase, and then using the separated organic phase in a plutonium recovery process.   
     
     
       2. Process as defined in claim 1 wherein the density of the electrolysis current at the anode is maintained below the density at which oxygen develops. 
     
     
       3. Process as defined in claim 1 wherein the anode material is platinum or a platinized metal with passivation properties and the cathode material is titanium. 
     
     
       4. Method as defined in claim 1 wherein the anodic oxidation takes place in one or a plurality of series-connected electrolysis cells without diaphragms, and said electrolysis cells are connected ahead of the extraction devices. 
     
     
       5. Process as defined in claim 1 wherein the anodic oxidation takes place in one or a plurality of series-connected electrolysis cells provided with diaphragms. 
     
     
       6. Process as defined in claim 1 wherein the anodic oxidation and the extraction of the plutonium takes place in an extraction device in which the aqueous solution and organic extraction agent circulate continuously in countercurrent flow. 
     
     
       7. Method as defined in claim 1 wherein together with the anodic oxidation of the Pu(III), hydrazine nitrate and hydroxyl ammonium nitrate in the aqueous solution are positively destroyed. 
     
     
       8. The method as defined in claim 1, wherein said aqueous nitric acid solution that is subjected to the electrolysis voltage is obtained by selectively extracting plutonium from an organic phase containing uranium. 
     
     
       9. The method as defined in claim 8, wherein said uranium-containing organic phase further contains neptunium. 
     
     
       10. The method as defined in claim 9, wherein said uranium and neptunium-containing organic phase contains fission products and, further comprising the steps of: i. after the selective extraction of the plutonium, transferring the uranium and neptunium to an aqueous nitric acid solution along with fission products, with the uranium and neptunium being present therein in a low oxidation state of U(IV) and Np(IV);   ii. subjecting said uranium and neptunium-containing nitric acid solution to an electrolysis voltage of about the voltage at which oxygen develops at the anode or higher to anodically oxidize the U(IV) to U(VI) and the Np(IV) to Np(VI);   iii. transferring the U(VI) and/or Np(VI) formed in step (ii) from the aqueous nitric acid solution to an organic phase by means of an organic extraction agent; and   iv. separating the organic phase formed in step (iii) from the aqueous nitric acid solution of step (iii).   
     
     
       11. A method for purifying actinides present in low oxidation states and selected from the group of uranium (IV), neptunium (IV) and mixtures thereof, said actinides being present in an aqueous solution containing fission products, by extracting the actinides from the aqueous solutions and confining the fission products to the aqueous solution, comprising subjecting a nitric acid solution containing the actinides, hydrazine nitrate or hydroxyl ammonium nitrate, and fission products to an electrolysis voltage of about the voltage at which oxygen develops at the anode or higher to anodically oxidize the U(IV) to U(VI) and the Np(IV) to Np(VI), transferring the U(VI) and/or Np(VI) formed by anodic oxidation from the aqueous phase to an organic phase by means of an organic extraction agent, separating the organic phase from the aqueous phase, and then using the separated organic phase in a uranium or neptunium recovery process. 
     
     
       12. Process as defined in claim 11 wherein the density of the electrolysis current at the anode is maintained above that at which oxygen is formed. 
     
     
       13. Process as defined in claim 11 wherein the anode material is platinum or a platinized metal with passivation properties and the cathode material is titanium. 
     
     
       14. Method as defined in claim 11 wherein the anodic oxidation takes place in one or a plurality of series-connected electrolysis cells without diaphragms, and said electrolysis cells are connected ahead of the extraction devices. 
     
     
       15. Process as defined in claim 11 wherein the anodic oxidation takes place in one or a plurality of series-connected electrolysis cells provided with diaphragms. 
     
     
       16. Process as defined in claim 11 wherein the anodic oxidation and the extraction of the actinides takes place in extraction devices in which aqueous solution and organic extraction agent circulate continuously in countercurrent flow. 
     
     
       17. Method as defined in claim 11 wherein together with the anodic oxidation of the actinides, hydrazine nitrate and hydroxyl ammonium nitrate in the aqueous solution are positively destroyed.